High-Temperature Vaporization of B2O3(1) under Reducing Conditions

The vaporization of B2O3 in a reducing environment leads to the formation of both B2O3(g) and B2O2(g). Whereas the formation of B2O3(g) is well understood, many questions about the formation of B2O2(g) remain. Previous studies using B(s) + B2O3(1) have led to inconsistent thermodynamic data. In this study, it was found that, after heating, B(s) and B2O3(1) appeared to separate and variations in contact area likely led to the inconsistent vapor pressures of B2O2(g). To circumvent this problem, the activity of boron was fixed with a two-phase mixture of FeB and Fe2B. Both second- and third-law enthalpies of formation were measured for B2O2(g) and B2O3(g). From these values, the enthalpies of formation at 298.15 K were calculated to be -479.9 +/- 25.7 kJ/mol for B2O2(g) and -833.4 +/- 13.1 kJ/mol for B2O3(g). Ab initio calculations to determine the enthalpies of formation of B2O2(g) and B2O3(g) were conducted using the W1BD composite method and showed good agreement with the experimental values.